Why do younger girls always look at me?

I notice younger girls normally will look over at me and check me out and I'm close to my mid twenties. The girls are normally between 14-17 years old. I normally don't have girls my age do this for some reason just younger girls. I will just ignore them because I even had these two young girls 15 or so years old walk by while I was in a line at the mall and they one girl looked at me and flirtatious said "whats up?" I just shook my head and smiled while she giggled to her friend. I have been told I look young before, like I'm 18 and also I get carded for a are movie a couple months ago :/. I can't help I look young but is this the reason why?
Why do younger girls always look at me?
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